Texas Thundercloud Caught on Video

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An ominous cloud formation that developed in the Texas panhandle
last week looks like a CGI effect straight out of a summer
blockbuster. This tornadic thunderstorm, which formed near the
town of Adrian during the evening of May 21 and gave rise to at
least one twister, offered passersby with video cameras an
exceptional view of nature's might.

Experts say the saucer-shaped cloud was the most severe type of
thunderstorm: a supercell. "What you are seeing here is a
well-developed rotating supercell thunderstorm, and the
condensation pattern at cloud base forms a 'belt' or 'wall'
appearance as air is lifted and sucked into the swirling storm,"
said Chris Walcek, a meteorologist at the Atmospheric Sciences
Research Center at the State University of New York, Albany.

Supercells form when a pocket of hot, vapor-filled air starts to
rise in the presence of just the right amount of "wind shear," or
change in wind speed with height. The huge air pocket starts to
rotate, and the Coreolis force generated by the spin of the Earth
enhances the air pocket's rotation. ( Astonishing
Video Shows a Face in the Clouds )

Judging by
the clear view the filmographers have of their subject, this
particular storm is most likely a "low precipitation (LP)
supercell," said Bill Cotton, professor emeritus of meteorology
at Colorado State University and an expert on cloud and storm
dynamics. These typically produce little rain, but lots of hail,
and while the process is not totally understood by scientists, "I
might speculate that the storm is ingesting large amounts of
pollution or dust, which would suppress the warm rain process and
result in the prevalence of hail," Cotton told Life's Little
Mysteries.

These relatively dry supercells are storm-chasers' favorite
variety of tornadic thunderstorm, because the lack of
view-obscuring rainfall means tornadoes and other impressive
cloud features can be seen from a safe distance. Walcek said,
"There is [usually] so much rain falling from these storms that
the cloud formations are hidden behind sheets of falling rain."